R - Rubber mounted engine (some models) racing version (other models) e.g. the FXR is a lowrider with rubber mounted engine, WLR is the flat track racer that was very hard to beat in the 30's, 40's, and 50's.

ST- Soft Tail

S - (without following T) Sports version eg FLHS is an FLHT without the touring package.

T - Touring

WG - Wide Glide

Sportsters:Models beginning with X are Sportsters. These descend from the K series, 1952-56. The XL series started in 1957. They are "unit construction" (engine & transmission share a common case). X was in the normal series, following the U and V used for flathead Big Twins. L stood for high compression (7.5:1 in 1957). In 1958 came the XLH with H meaning Higher-power or High-compression (9:1) or Hot. Also in 1958 was the XLCH: The C in XLCH was intended to mean "Competition", but the late Hal Robinson used to claim the CH on his bike stood for "Charley Horse" because it was highly modified and had enough initial ignition advance to kick back rather severely.

The Sportster engines were originally actually 53.9ci. (883cc) but were designated as 55ci. This was upgraded (in 1970?) to 61ci (1000cc), redesigned in '73 but still 61" and stayed relatively unchanged untill the 74" evo version. The 883 and 61" were both produced the first year of the 883. Options for Sportsters abounded but these same letters have been used since 1958 in various combinations, plus the XLCR (a "cafe racer" style, with bikini fairing) and the XLT (Touring, with bigger tank, thicker seat, and hard bags straight off the FLHS), both produced 1977-1978 only.

Big Twins: Models beginning with F are Big Twins. These all descend from the 61E in 1936. Knuckleheads 1936-47, Panheads 1948-65, Shovelheads 1966-84/85, and Evolutions 1984/5-present. The Evolution (block head) was introduced in '84 on the Soft Tail and Tourglide Ultra, with the last Shovel built in mid '85. Until 1978, these were mostly 74's (~1200cc). In 1978, the 80ci (~1340cc) was introduced.

In 1971 was the first FX model, with an F engine and assorted Sportster (X) parts, notably forks - these were initially Super Glides. In 1974, FXE was Electric start. In calendar 1977 came the FXS Low Rider, with shortened shocks and scooped seating position. Also in 1978, the FX Super Glides got belt final drive. 1979 brought 80ci Shovelheads and the FXEF Super Glide Fat Bob (not Boy), for bobbed fenders and fat tank. In 1980, FXWG (Wide Glide) andthe FXB Sturgis with belt drive (primary and secondary).

1984 brought the Softtail FXST, with the look of an old hardtail but some suspension for comfort.

In 1991 came the FXD Dyna Glide series, starting with another Sturgis model. This brought many frame and engine mounting changes, a relocated oil tank and moved crossover pipe.

Touring:In 1980, the FLT designation was introduced for the Tour Glide. This model introduced the vibration-isolation mounted engine (rubberglide) and also a slightly different frame from other FLs and a fixed fairing. FXR (originally called Super Glide II) arrived in late 1981. The R had rubbermount engine and 5-speed tranny, as opposed to rigid-mount and 4-speed in other models. FXRS maybe meant Sport, with cast wheels and a small sissy bar. The Sport Glide FXRT (Touring) arrived in 1983, with the fixed fairing and air adjustable anti-dive forks.

The only really reliable letters now are at the beginning of the model: X=Sportster, F=Big Twin, FL=Big Twin with big forks, FX=Big Twin with Sportster-style (smaller) forks, FXST=Softtail, FXD=Dyna Glide. At times, different models have even shared the same letter-designation; witness the FLHTC Electra Glide Classic/Ultra Classic Electra Glide in 1993 models.